The present invention relates generally to providing an electrically shielded cover for a packaged optical device. More particularly, the present invention relates to providing an electrically shielded glass lid for an optical micro electromechanical system (MEMS) package.
Conventionally, semiconductive wafer based devices such as optical micro electromechanical systems (xe2x80x9cMEMSxe2x80x9d) are produced using a variety of methods of fabrication. Notwithstanding the process of fabrication, the produced MEMS requires a cap or lid to protect the MEMS from environmental insult, such an undesirable humidity. Such caps have been typically glass lids that provide both the environmental protection and provide an optical window for the optical devices in a MEMS package.
However, conventional glass lids have one disadvantage in that conventional glass lids are typically dielectrics that can have electrostatic energy build up upon them. The built up electrostatic energy can result in an electrostatic discharge that can damage the optical MEMS devices. Moreover, the build up of electrostatic energy can produce local electrical fields that may distort the optical MEMS devices, especially if these devices are sensors.
In one solution to counter this disadvantage, a conventional glass cover would be located far enough from the optical devices so that the air gap would be large enough to prevent a discharge. Moreover, the large air gap would cause the locally generated electrical fields to be minimally weak around the optical devices. Although these conventional devices would provide an optical device shielded from the environment and protect from electrostatic discharge and locally generated electrical fields, the package surrounding the optical device would large and thus costly and not small enough to be used in many applications. Furthermore the large air gap creates a long optical or focal length that could keep the optical device from being used in certain applications.
In another solution to counter this disadvantage, a conventional glass cover would be covered with a thin transparent film of transparent electrodes. The transparent electrodes provide an electrical path for the electrostatic energy to be drained off the glass cover. Although the transparent electrodes provide protection against electrostatic insult to the optical device, the transparent film and transparent electrodes are not absolutely transparent. Using such a solution for electrostatic protection causes undesirable light loss. Such light loss is unacceptable in such applications as fiber optic telecommunication systems. More specifically, telecommunication applications using optical communication are starved for light due to light loss along the fiber optic network, thus any light loss, even a small percentage of loss, can significantly impact the application in a negative manner.
Moreover, the use of transparent electrodes and thin films hinders the use of optical MEMS devices with certain wavelengths of light. For example, some transparent electrodes do not transmit well in the UV spectrum. This is significant when the optical MEMS devices may be used in conjunction with an EPROM that uses UV light to enable programming of the EPROM.
The present invention provides a glass lid for an optical MEMS package, while avoiding the disadvantages of the conventional devices. More specifically, the present invention prevents an electrostatic discharge and reduces or eliminates any undesirable locally generated electrical fields. The present invention also provides protection from the environment, such as humidity, while providing an optical window for the optical MEMS devices wherein the light loss is greatly reduced to-an insignificant level or eliminated. Lastly, the packaging of the optical MEMS is greatly reduced by the present invention, thereby reducing costs and expanding the applications for the optical MEMS package.
One aspect of the present invention is a packaged device. The packaged device includes a package substrate; a plurality of optical structures formed on a semiconductive substrate and positioned on the package substrate, forming an active area; a contiguous solderable seal structure surrounding the plurality of optical structures; and a cap formed over the plurality of optical structures and upon the contiguous solderable seal structure. The cap has, formed thereon, patterned metalization. The patterned metalization is located over the active area.
Another aspect of the present invention is a metalized glass lid for an optical die. The metalized glass lid includes a glass portion and a metalization adjacent to the glass portion. The metalization has clear apertures and is connected to a DC voltage.